First of all, install the three Unofficial Oblivion patches (vanilla + KOTN & DLCs + SI).
About combat: Oscuro Overahul, Francesco's and Deadly Reflex if you're going melee a lot, up to you.
UI: Darnified Ui is the best I think, it improves the standard interface in many ways, altough it leaves the main structure.
Map: there are several Map mods at TESNexus, like Elven Cartographers which is very good.
These are the first that came in my mind.